1. Field of the Invention
The present invention relates to turbines and particularly to a locking device for locking rotor blades circumferentially to a rotor.
2. Description of the Prior Art
It is well known in the prior art to mount rotor blades in a circumferential groove provided on the spool or rotor disc of a compressor or turbine rotor in a gas turbine engine. The groove includes a relatively narrow throat defined by inwardly extending flanges. The blades have hammerhead-shaped roots adapted to slide in the grooves and be retained against centrifugal force by the flanges. A stacking hole is provided extending radially through the flanges and communicates with the groove. The stacking hole is large enough to accommodate the hammerhead-shaped root portion of the rotor blade. The problem is to lock the rotor blades in the groove, considering the stacking hole, in a manner to retain the blades against circumferential movement which can be caused by the tangential component of force when the rotor is turning at high speeds.
Such a locking device is illustrated in U.S. Pat. No. 3,088,708, Feinberg, May 7, 1963, which shows the use of a block in combination with a set screw, which set screw bears against the bottom of the groove while maintaining the block in an upward position locked against the platforms of the blade and the flanges or shoulders defining the throat of the slot.
Another locking device is illustrated in U.S. Pat. No. 3,597,112, Garten, Aug. 3, 1971. In the Garten patent, a spring retaining slot is provided, subsidiary to the circumferential root receiving slot. The ends of a leaf spring engage the ends of the spring retaining slot, and a protuberance engages between the root members of a pair of blades straddling the stacking hole.
U.S. Pat. No. 3,955,898, Zaehring, May 11, 1976, shows a spring operated locking device having a swivel portion adapted to be rotated once it is in the slot to register with the stacking hole.
All of these locking devices are believed to work satisfactorily with relatively large engines. However, they become impractical when applied to very small gas turbine engines, such as the Pratt & Whitney PT6 type, where the compressor rotor may be in the order of 5 inches in diameter.
When assembling such small rotors, it is not practical to utilize coil springs or set screws as the present above-mentioned locking devices.